Impact wrench



Dec. 3, 1968 w, W L 3,414,066

IMPACT WRENCH Filed Aug. 31, 1966 INVENTOR. W/lZ/fl/V ll. will!!! sw d Dec. 3, 1968 v w. K. WALLACE IMPACT WRENCH 4 Sheets-Sheet 5 Filed Aug. 31, 1966 V INVENTOR. W/ZZ/l/Y M Will/(i W. K. WALLACE IMPACT WRENCH Dec. 3, 1968 4 Sheets-Sheet'4 Filed Aug. 31, 1966 INVENTOR W Z (/41 K. 414411.403

BY J t ATTORNEY United States Patent 3,414,066 IMPACT WRENCH William K. Wallace, Barneveld, N.Y., assignor to Chicago Pneumatic Tool Company, New York, N.Y., a corporation of New Jersey Filed Aug. 31, 1966, Ser. No. 576,368 16 Claims. (Cl. 17393.6)

ABSTRACT OF THE DISCLOSURE A impact wrench is disclosed having a rotating dog that is periodically movable axially against a return spring into impacting relation with an anvil when a cam carried by the dog has cooperation with a ball rollable about a track defined between the dog and an extension of the anvil. The cam is cooperable with the ball only when the ball is located in a particular area of the track. The ball is caused to be rolled about the track to the particular area by means of a friction ring carried by the dog, and is then released of the ring as it enters the particular area. During a cam action the ball is forced over an abutment in its path into a relatively deep area of the track where, following an impacting action of the dog with the anvil, the ball is again frictionally gripped by the ring and again rolled about the track.

This invention is concerned with improved camming means in an impact wrench for causing repeated reciprocation of rotating hammer driven means into forceful impacting relation with a torque output anvil either in a positive or reverse direction to tighten or loosen threaded fasteners, such as bolts and nuts.

The camming means is of a type which includes a ball member rollable about a track relative to a pair of opposed cam elements which cooperate with the ball to advance the hammer driven means into impacting relation with the output anvil.

The improved structure'and arrangement of the camming means represents a desired technical advance in this art. One advantage of it is that the cooperation of the cam elements with the ball is such that hammer driven means carrying one of the cam elements is permitted to be advanced with an accelerated force into impacting relation with the output anvil. Another advantage is that no lost motion connection is required between either cam element and the means by which it is driven to obtain positive or reverse directional operation of the tool.

A still further advantage of the improved camming means is that it permits two revolutions of motor acceleration before the device delivers an impact blow to the work. This action serves to increase the operating speed of the motor with resultant increased impacting intensity. The improved camming means, though subject to wide application, is especially suitable for use in work situations wherein high speed as well as powerful impact blows are desired.

In accordance with the invention, there is provided an impact wrench including a torque receivable anvil; a torque transmitting rotatable dog periodically cammable axially into torque transmitting relation with the anvil; cammable means unitary with the anvil including an annular ball track, a ball rollable therein and an abutment in the path of the ball adapted to arrest rolling of the ball about'the track; a cam carried by the dog having rotation with the dog relative to the abutment, but having camming cooperation with the ball when the ball is arrested by the abutment to simultaneously cam the dog into torque transmitting relation with the anvil and to force the ball over the abutment; friction means carried by the dog having engagement with the ball to roll it Patented Dec. 3, 1968 over the track onto the abutment; and means causing release of the ball from the friction means when the ball has engaged the abutment.

In the accompanying drawings illustrating an embodiment of the invention:

FIG. 1 is a longitudinal section of an impact wrench showing a hammer driven dog in normal retracted position and the cam ball in the deep area of the ball track, parts of the wrench unnecessary to its understanding being broken away;

FIG. 2 is a fragmentary view of FIG. 1 but showing the ball and dog in a position at the start of a camming action;

FIG. 3 is a further fragmentary view of FIG. 1 but showing the dog advanced by a camming action into impact relation with the anvil;

FIG. 4 is a rear end detail view of the dog;

FIG. 5 is a front end detail view of the dog;

FIG. 6 is a detail of the jaw face of the anvil;

FIG. 7 is a detail view in elevation of the cam shaft;

FIG. 8 is a left end view of FIG. 7;

FIG. 9 is an enlarged section on line 99 of FIG. 8;

FIG. 10 is an enlarged view of a fragment of FIG. 7 rotated counterclockwise;

FIG. 11 is an enlarged section on line 11-11 of FIG. 9;

FIGS. 12 to 16 are schematic views, in which FIGS. 12 and 13 correspond to FIG. 2 and show the ball on an inside radius of the ball track of the cam shaft and the cam of the dog at the start of a camming action;

FIG. 14 shows the dog advanced into impact relation with the anvil;

FIG. 15 shows the dog in retracted position following impact;

FIG. 16 shows the ball being guided back into the deep area of the ball track following the impact action;

FIG. 17 is an elevational view of a modified form of the timing cam shaft;

FIG. 18 is a section on line 18-18 of FIG. 17;

FIG. 19 is a schematic view corresponding to that of FIG. 12, but showing the tool as having the modified form of timing cam shaft; and

FIG. 20 is a sectional schematic detail showing the ball in a slot of the cam shaft during the occurrence of an impact action.

The impact wrench disclosed in the drawings illustrating the invention includes a general housing 21 in which is supported a pneumatically powered motor of the conventional slidable blade type, a driving shaft portion of which is indicated at 22. The motor has a splined driving connection at 23 with an axially extending hub 24 of a rotatable hammer or mass 25. The hammer is cup-form, having a cylindrical skirt or barrel portion 26. The latter is open at its forward end; and it is closed at its rear by a back wall 27. The hammer is supported for rotation in a pair of oppositely arranged bearings 28 and 29; and is restrained by these hearings against axial movement. The hammer has an internal straight splined driving connection at 31 with a tailpiece 32 of a rotatable impacting dog 33. This connection enables axial slidable movement of the dog relative to the hammer. The dog has a normal or retracted position as in FIG. 1 wherein its tailpiece is received within the interior of the hammer and abuts the backwall 27. A head portion of the dog projects beyond the hammer and has on its forward face a pair of diametrically opposed anvil impacting jaws 35 (FIGS. 1, 5). A yieldable return spring 36 constantly urges the dog to its retracted normal position. During operation of the tool, the dog is adapted to be periodically advanced axially by camming means, generally indicated at 37, against the resistance of spring 36 into impacting relation with an anvil 38.

The anvil is journaled for rotation in a bushing 39 fitted in a nosed end 41 of the housing. The anvil has an external shank end 42 adapted for driving connection with a work socket (not shown). The socket is suited for drivingly engaging work, which may be a bolt head, nut, or other threaded fastener. Internally of the housing, the anvil has a pair of diametrically opposed torque impact receiving jaws 43 (FIGS. 1, 6). An annular lip 44 of bushing 39 spaces the anvils jaws a desirable distance inwardly of the wall of the housing. The anvil is restrained against axial movement in a forward direction relative to the housing by means of the bushing 39; and is restrained against axial movement in the opposite direction by means of a timing shaft or cam shaft 45 (FIGS. 1, 7).

The cam shaft is axially aligned with the anvil and is coaxial with the dog and hammer. It has a rear hub 46 supported for rotation in the bearing 29. The cam shaft is restrained by this hearing against axial movement in a rearward direction. The cam shaft extends through an axial bore 47 of the dog, and has a pilot end 49 seated in a complementary axial bore of the anvil whereby the cam shaft is restrained against axial movement in a forward direction. The pilot end of the cam shaft is rigidly keyed at 51 to the anvil 38 whereby each is restrained against relative rotation and both are rotatable together as a unit. The dog return spring 36 surrounds the cam shaft and is seated at its forward end in a counterbore 52 of the anvil. The opposite end of the spring abuts a bushing 53. This bushing is fitted in the front end of the bore 47 of the dog, and slidably sleeves a smooth cylindrical surface of the cam shaft. A lip 54 of bushing 53 abuts a forward face of the dog. This bushing serves to support the dog for axial sliding movement as well as rotation relative to the cam shaft. The cam shaft has adjacent its hub 46 a cylindrical enlargement 55 slidably received in a rear counterbore 57 of the dog.

The dog is normally held clear of the jaws of the anvil by means of the return spring thus providing clearance 58 as seen in FIG. 1. The dog has a position advanced against the resistance of the spring, wherein its jaws 35 are received between the jaws 43 of the anvil, as in FIG. 3. If the dog is rotating in a positive direction while acquiring this advanced position, the sides 59 of its jaws (FIG. will forcefully impact against corresponding sides 59a of the jaws of the anvil (FIG. 6); and if the dog is rotating in a reverse direction, the other sides 61 of its jaws will impact against corresponding sides 61a of the jaws of the anvil. The camming means 37, between the dog and the cam shaft, function during operation of the tool to periodically forcefully advance the dog into i-mpacting engagement with the anvil against the resistance of the spring 36; and following the impacting action this spring automatically functions to return the dog to its retracted position. The camming means is designed to operate so that one impact blow is delivered by the dog to the anvil during every other revolution of the dog.

The camming means 37 includes an annular ball track 62 formed on a shoulder of the cam shafts (FIGS. 1, 7- 12); an opposed annular cam track 63 formed on a shoulder of the dog (FIGS. 1, 4); a raceway 64 around the cam shaft adjacent the ball track 62; and a ball 65 rollable on the raceway between the tracks 62 and 63.

The ball track 62 of the cam shaft comprises a symmetrical camming surface 66 (best seen in FIGS. -12) extending substantially over 180 of the track to the left of line AA in FIG. 11; and a grooved or deep portion 67 arcuate in crosssection, extending over the remaining 180 of the track. The camming surface 66 includes a pair of ramps 68, 69 which rise axially and progressively toward each other from corresponding ends of the deep portion 6 7 of the track. Ramp 68 merges at a point of tangency with an inside radius 71; and the other ramp merges at a corresponding point of tangency with. a similar inside radius 72. The inside radii 71, 72, in turn,

merge at their high ends into an outside radius to define a cam lobe 73.

The raceway 64 extends around the cam shaft adjacent the ball track. The ball is confined or held captive in the raceway as it rolls relative to the ball track. The raceway has a symmetrical wide area 74 which is centered opposite the cam lobe 73 and extends equally to either side for a distance greater than here for approximately This wide area allows for free but limited axial movement as well as limited circumferential movement of the ball 65 after it leaves the ball track following a camming action, as will later be described. It is limited in this free movement by a radial stop 75 bounding the wide area 74. The wide area communicates at opposite ends with a relatively narrower section 76 of the raceway. Following a camming action, a lug 77 serves to guide the ball into this narrow section and back into the deep portion 67 of the ball track. This narrow section 76 is diametrically opposite the cam lobe 73.

The dog cam track 63 (FIG. 4) includes a grooved section 78 arcuate in cross section; and a relatively short symmetrical cam tooth 79 defined by a pair of inside radii 81, 82 rising progressively axially toward each other and merging into an outside radius or crest. The cam tooth 79 corresponds substantially to the cam lobe 73 of the ball track, except that the outside radius of the cam tooth is slightly less than that of the cam lobe.

When the dog is in its fully retracted condition, as in FIG. 1, and the ball 65 is located in the ball track 62 beyond either of the inside radii 71, 72 of the cam lobe 73, the cam tooth 79 of the dog will pass clear of the ball as the dog rotates. But, when the ball is located on an inside radius of the ball track, it will be engageable by the cam tooth of the dog, as appears in FIGS. 2, 12, 13.

The function of the ramp portions 68, 69 of the ball track 62 is to guide the ball, accordingly, as the ball is rolled in a selected direction onto an inside radius 71 or 72 where it will be engageable by the cam tooth 79 of the dog to effect axial advancement of the dog into impacting relation with the anvil. When the ball attains a position on the inside radius 71 of the cam lobe 73 as in FIGS. 12, 13, it will be cooperable with a corresponding point on the inside radius 82 of the cam tooth 79 for the start of a camming action, as the dog rotates in a positive direction; and when the ball is in a corresponding position on the other inside radius 72 of the cam lobe, it will be cooperable with a corresponding point on the other inside radius 81 of the cam tooth as the dog rotates in a negative direction.

The wide area 74 (FIGS. 10, 11) of the raceway 64 of the cam shaft is interrupted by a low or relieved area 83 centered opposite the cam lobe 73 and extending symmetrically for several degrees angularly to either side of the lobe substantially to points opposite the start of the inside radii 71 and 72, as indicated by lines B and C. When the ball has attained a position on either of these inside radii, it will also have attained a position in the relieved area 83.

A resilient ring 84 (FIGS. 1-3), preferably of rubber or equivalent, positioned coaxial with the dog and the cam shaft, is seated fast in an annular internal groove of the dog adjacent the dog track 63. As the dog rotates and carries this rubber ring, the latter frictionally engages the ball 65, as appears in FIG. 1, except when the ball is in the relieved area 83, and rolls the ball over the ball track 62 and the raceway 64 of the cam shaft until the ball enters the relieved area. When the ball is in the relieved area, the rubber ring will pass clear of it, as appears in FIG. 2.

The operation of the tool is as follows (FIGS. 1-3, and 12-16): After the output end 42 of the tool is applied to a workpiece, such as the hexagonal head of a threaded bolt, clockwise rotation of the motor 22 is then transmitted through the hammer 25 to the dog 33. Since the ball 65 is normally in the ball track 62 beyond the inside radii of the cam lobe 73, it will be frictionally engaged by the rubber ring and rolled by the latter over the ball track and the raceway toward the ramp 68. Eventually, the ball will be rolled by the rubber ring off the ramp simultaneously onto the inside radius 71 and into the relieved area 83. As the ball enters the relieved area it drops free of the rubber ring (FIG. 2), and the cam tooth 79 of the dog eventually attains the position shown in FIGS. 12 and 13 at high speed. The ball is then rolled by the inside radius 82 of the rotating dog into contact with the inside radius 71 of the ball track. But, at this time due to the free running condition of the work, the cam tooth 79 of the dog is prevented by the resistance of spring 36 from forcing the ball up the cam radius 71 of the ball track. Accordingly, the work is run down to an initial degree of tightness as the anvil 38 and cam shaft 45 are forced to rotate with the dog. Upon this initial tightness being attained, the increased resistance of the work causes the dog to rotate relative to the now stationary anvil and cam shaft. In this relative rotation, the two opposing cam surfaces defining the inside radii 82 and 71 act through the ball to provide a camming action that accelerates the dog 33 axially toward the anvil 38 into full engagement with the latter followed by a forceful impacting action of the jaws of the dog with those of the anvil. In this camming action, the, cam tooth 79 of the dog forces or shoots the ball over the cam lobe and loses con-tact with it as the dog moves axially into engagement with the anvil; and the rubber ring 84 is carried by the dog axially clear (FIG. 3) of the path of the ball, the latter upon moving over the cam lobe, rolls into the wide area of the raceway. The ball at this time will be out of the ball track and lie in the wide area 74 of the raceway somewhere between the relieved area 83 and the raised stop lug 77. Next, upon dissipation of the energy of the impact, spring 36 re-expands to return the dog to its retracted position (FIGS. 1, 15). In this return movement of the dog, the rubber ring 84 rides axially over the ball and rolls it axially toward the ball track. Then, upon retraction of the dog, the latter resumes its rotation, and as it does so the rubber ring 84 forces the ball against the stop guide lug 77. The latter acts to guide the ball back into the deep portion of the cam track, as appears in FIG. 16. At about this time, as the ball is being rolled by the rubber ring back into the ball track, the cam tooth of the dog cooperates in this action as it rides over and clear of the ball, and then advances ahead of it. Since the cam tooth 79 of the dog is being advanced relative to the ball track at a faster rate than the ball is being rolled over the track by the rubber ring, the cam tooth 79 of the dog will pass clear of the cam lobe 73 to complete one revolution without an impact action taking place. This revolution will be completed before the ball has been again rolled onto the inside radius 71 preparatory to a further camming action. However, during the subsequent or second revolution of the dog, the ball will have been eventually rolled by the rubber ring up the ramp 68 into the relieved area 83 and onto the inside radius 71 to the position shown in FIG. 1. This will occur before the cam tooth 79 of the dog attains the position shown in FIGS. 12 and 13. When the FIGS. 12 and 13 position of the dog and ball track is attained, a camming and consequent impact action again occurs, the impacting action occurring upon revolution of the dog relative to the cam shaft and anvil. The operation of the tool continues following retraction of the dog after an impact action to repeat the impact upon every other revolution of the dog.

Explaining the camming action in further detail, when the ball obtains the position of FIGS. 12 and 13, the two cam surfaces 71 and 82, which are in the form of large inside radii, coperate with the ball in accelerating the dog axially toward the anvil. The profile of the cam lobe 73 associated with the anvil changes from a large inside radius 71 to an outside radius defining the crest portion of the lobe before the profile of the cam tooth 79 of the dog does. By the time the point of contact of the ball has been moved to the point of tangency of the inside radius 71 with the outside radius of the cam lobe 73, the dog will have been accelerated to a high axial velocity to carry it into full engagement with the anvil. In this action, the point of contact of the ball is caused to move beyond this point of tangency; and, as it does so, the angle of action of the cam forces upon the ball exceeds the angle of friction so as to shoot the ball over the crest of the cam lobe 73.

The tool operates similarly when the motor is operated in a reverse direction, except that the other inside radii 81 and 72 respectively of the dog and ball tracks cooperate with the ball in advancing the dog into impacting relation with the anvil. It is to be noted that the cam track 63 of the dog and the ball track 62 of the cam shaft are respectively integral with the dog and cam shaft, and that no lost motion connection is required in this structure to enable reverse operation of the tool. This advantage is due to the structural arrangement of the jaws and cam elements of the dog and cam shaft. In this respect, the cam lobe 73 of the cam shaft 45 is centered relative to the space S between the anvil jaws 43, as indicated by the line PP; and the cam tooth 79 of the dog is centered relative to its jaws 35 (FIG. 13), as indicated by the line DD. The angular spaceing S between the anvil jaws 43 corresponds to that betwen the jaws of the dog. It is also to be noted that the angular space between the anvil jaws is relatively greater than the angular expanse of the jaws 43 of the dog. Here, the spacing from one anvil jaw to the next is at least twice the expanse of one of the jaws of the dog. During camming action in this arrangement, the cam tooth 79 of the dog will pass over the cam lobe 73 of the cam shaft at a time when the jaws 35 of the dog are substantially centered relative to the spacing S of the anvil jaws, whether the dog is rotating in a positive or negative direction. The angular space available in which to move the dog axially into engagement with the anvil is equal to the angular space S, as shown in FIG. 6, less the angular space occupied by the jaw of the dog. Due to the radii 80 and respectively on the corners of the dog and anvil jaws, it is possible to start the axial movement of the dog slightly before the jaw 35 of the dog is angularly clear of the anvil jaw 43, as shown in FIG. 13.

It is understood that instead of the keyed engagement at 51 of the cam shaft with the anvil, the pilot end of the cam shaft may be splined as indicated at 49a in FIG. 17 so as to have a splined engagement with the anvil.

The cam shaft 45 may take the form shown at 45a in FIGS. 17-20. In this form, there is provided in lieu of the wide relieved area 83 and the guide lug 77, both shown in FIGS. 10 and 11, a pair of identical parallel slots 87 and 88 separated by an angular guide surface 89 in the peripheral surface of the cam shaft adjacent the ball track 62. The guide surface 89 is centered opposite the cam lobe 73. And the slots 87, 88 are spaced equally to either side of the cam lobe and opposite the corresponding inside radii 71 and 72, so that when the ball 65 has attained a position on either of the inside radii it will also have attained a position in the corresponding slot. The peripheral area of the cam shaft adjacent the angular guide surface 89 is defined by a shallow groove 91 over which the ball is rollable from one slot to the other. When the ball lies in either slot, it will be free of the rubber ring 84 carried by the dog; but when the ball is in the shallow groove 91 between the slots it will be frictionally engaged by the rubber ring.

The operation of the tool having the modified cam shaft 45a is substantially the same as when the cam shaft 45 of FIG. 7 is used, but differing in the manner of movement of the ball 65 during the camming action.

During operation of the tool having the modified cam shaft 45a, when the ball has been rolled by the rubber ring 84 of the dog to the inside radius 71, it becomes free of the rubber ring as it drops into the slot 87. It remains in the slot until it is picked up by the cam 79 of the relatively rotating dog 33a. The cam surfaces 82 and 79 of the dog cooperate with the ball to force it out of the slot and shoot it over the opposed cam lobe 73. As the ball is being forced by cam 79 out of the slot, it will be frictionally gripped by the rubber ring 84 and rolled over the shallow groove 91 into the next slot 88 where it will become free of the rubber ring, being guided in this movement by the angular surface 89. In the camming action, the dog is forced (as earlier described) axially into impacting engagement with the jaws of the anvil 38. The ball remains in slot 88 during the impact action, as indicated in FIG. 20. Following impact, the dog is rapidly returned out of impacting relation by the force of the return spring, causing the ball to be rapidly moved along slot 88 and up the inside back radius 92 thereof into the ball track 62 and into contact with the rubber ring 84 of the dog. Upon engaging the rubber ring, the ball is advanced by the latter out of the slot, and is again rolled about the ball track as earlier described herein.

What is claimed is:

1. In an impact wrench including a rotary driving mass, a driven torque output anvil, a dog drivably connected with the mass having movement relative thereto into and out of clutched engagement with the anvil, and a yieldable spring constantly urging the dog out of such engagement; the improvement comprising an extension of the anvil, an annular track between the extension and the dog having a ball rollable therein, an obstruction on the extension projecting into the track upon which the ball is limitable, a cam carried by the dog having rotation with the dog clear of the ball before the ball is limited by the obstruction but having engagement with the ball only when the ball is limited upon the obstruction so as to force the ball over the obstruction as the dog rotates relative to the extension of the anvil with the result that the dog is formed against the spring into such clutched engage ment by the ball, and means independently of the cam carried by the dog for rolling the ball about the track onto the obstruction.

2. In a impact wrench as in claim 1, wherein the means for rolling the ball about the track is a resilient rubber ring adapted for frictional engagement with the ball so as to roll it around the track onto such obstruction.

3. In an impact wrench including a driven clutch member having an axial extension, a torque impact transmitting driving member, a dog carried by the driving member having axial movement along the extension into and out of clutched impacting engagement with the driven member, and yieldable spring means constantly urging the dog out of clutched engagement; camming means operable as the dog rotates relative to the driven member to advance the dog axially into such engagement, comprising: a cam tooth projecting axially from an annular shoulder of the dog, an annular ball track formed on an opposed shoulder of the extension having a deep area and a symmetrical surface rising axially from corresponding ends of the deep area to a cam lobe, the lobe having a round crest, the symmetrical surface including a pair of inside radii defining opposite sides of the lobe and further including a pair of ramps sloping from the inside radii down to the deep area of the track, a ball rollable about the track, the cam tooth of the dog having a normal position relative to the track, in which position the ball is out of the path of rotation of the cam tooth when it is in the ball track beyond the inside radii and extends in part in said path when it is on a selected inside radius accordingly as the dog is rotating in a selected direction, and means carried by the dog having frictional engagement with the ball while the ball is in the cam track beyond the inside radii so as to roll the ball about the track, a selected ramp of the symmetrical surface serving to guide the ball in its rolling movement out of the deep area of the track onto the selected inside radius, so that when the ball is on the selected inside radius it is caused to be cammed by the cam tooth over the lobe as the dog rotates and the dog is simultaneously forced thereby along the extension into clutched engagement with the driven member.

4. In an impact wrench as in claim 3, wherein the dog includes a pair of diametrically opposed clutch jaws, the center of the cam tooth lies in a radial plane extending through the center of the jaws of the dog, and the driven clutch member includes a pair of diametrically opposed clutch jaws between which the jaws of the dog are receivable, and the cam lobe lies in a radial plane extending midway between the corresponding clutch jaws of the driven clutch member.

5. In an impact wrench as in claim 3, wherein the means carried by the dog having frictional engagement with the ball is a resilient ring.

6. In an impact wrench as in claim 5, wherein the ball is of relatively smaller diameter than the inner diameter of the resilient ring so that the cam tooth of the dog is caused to be carried by the dog through a complete revolution of the dog before the ball has been rolled by the resilient ring through a complete revolution.

7. In an impact wrench as in claim 5, wherein there is a relieved area in the extension adjacent the lobe, the relieved area being so arranged that when the ball is rolled onto the selected inside radius of the lobe it is also simultaneously rolled into the relieved area wherein it automatically drops clear of the resilient ring.

8. In an impact wrench as in claim 7, wherein the cam tooth has a round crest and opposite sides of the tooth are defined by inside radii.

9. An impact wrench including a driven anvil having a pair of diametrically opposed torque impact receiving jaws and further having an axial extension beyond the jaws, a rotary driving member, a dog carried by the driving member having a pair of diametrically opposed torque impact transmitting jaws, the dog being slidably supported upon the extension and having axial movement in the driving member so as to carry its jaws into and out of impact transmitting relation with the jaws of the anvil, yieldable spring means constantly urging the dog out of such relation, means for moving the dog axially against the spring means and in a selected rotative direction to transmit torque impact through its jaws to those of the anvil, said means including a body of the dog and axially projecting cam tooth having symmetrical sides, and opposed annular ball track on a face of the extension including a ball rollable about the track, the track having an axially projecting cam lobe defined by opposed symmetrical inside radii, wherein the ball lies in the path of rotation of the cam tooth only when the ball is on a selected inside radius of the cam lobe so that upon the cam tooth engaging the ball the latter is forced over the lobe and the dog is simultaneously advanced axially to carry its jaws into torque transmitting relation with those of the anvil; characterized in that the cam lobe lies in a radial plane extending through a point midway between the anvil jaws, and the cam tooth lies in a radial plane extending through the center of the jaws of the dog.

10. An impact wrench as in claim 9, wherein a rubber ring carried by the dog is frictionally engageable with the ball so as to roll the latter about the track.

'11. An impact wrench as claimed in claim 10, wherein a relieved area is formed in the extension adjacent the cam lobe so arranged that when the ball is rolled onto a selected inside radius of the cam lobe it also enters the relieved area and becomes released from the rubber ring.

12. An impact wrench including a torque receivable anvil; a torque transmitting rotatable dog periodically cammable axially into torque transmitting relation with the anvil; cammable means unitary with the anvil including an annular ball track; a ball rollable therein and an abutment in the path of the ball adapted to arrest rolling of the ball about the track; a cam carried by the dog having rotation with the dog relative to the abutment, but having camming cooperation with the ball when the ball is arrested by the abutment to simultaneously cam the dog into torque transmitting relation with the anvil to force the ball over the abutment; and friction means carried by the dog having engagement with the ball to roll it over the track onto the abutment, and means causing release of the ball from the friction means when the ball has engaged the abutment.

13. An impact wrench as in claim 12, wherein the means causing release of the ball from the friction means is a slot opposite one side of the abutment adapted to receive the ball.

14. An impact wrench as in claim 13, wherein a second similar slot parallel to the first mentioned slot is positioned adjacent the opposite side of the abutment adapted to receive the ball after it has been forced over the abutment.

15. An impact wrench as in claim 14, wherein a shallow angular groove centered opposite the abutment connecting slots has an angular surface engageable with the ball so as to guide it from one slot to the other.

16. An impact wrench as in claim 15, wherein the ball is frictionally engageable by the rubber ring when the ball is located in the angular groove.

References Cited DAVID H. BROWN, Primary Examiner. 

